If asked now whether that work (which was more extensive, expensive and painful than I had bargained for) was needed or worth it, I would rationalise it on different grounds. I now see it as enabling a healthier atmosphere better able to regulate humidity in the bedrooms upstairs - breathing walls, fireplace ventilation restored to two bedrooms etc. I do also think the bedrooms will feel warmer than when their walls were entombed in cement but I couldn't quantify or prove this. The final validation of the decision to bring the kangos into the bedrooms was a nasty surprise that got revealed when we did: some of the upstairs floor joists were rotting under areas of cement!
We knew from the work done in 2014 that the one wall in the house - top to bottom - which hadn't been cement plastered internally was the south facing front wall. We think this was because it bowed slightly and cement-loving bungalow builders 15 years ago liked their straight lines and so built a straight stud wall covered with a light cement skim. We had peeked behind it in '14 when popping the windows out for repair and thought it would be a simple matter of taking down the stud and then lime plastering the wall behind. Had I looked closely behind the radiators under the windows (or just knocked on that section of wall), I might have realised that it wasn't all stud.
|Internal view of south-facing front wall in one of the bedrooms|
|2014... in the process of popping out the windows revealing the stud walls|
Sometime in April, I got a call at work from Kevin who was ripping out the stud: 'John there are poured cement sections of wall under the windows - do you want them kangoed out as well?'. My answer was yes. There then followed the call with the bad news: 'John the joists under the poured cement are rotten'.
As Kevin pointed out to soften the bad news, the positive thought was that we were discovering this now rather than 10 years later when it would be much worse. So what to do? First, understand why they rotted. Then agree a fix which we would be confident would not risk recurrence. As usual I turned to Pete Ward for advice.
Why they were rotting was fairly easy to deduce. Rain from the prevailing southwesterlies was getting in through micro cracks in the old external cement render and getting trapped between the thin section of stone wall under the window and the poured cement wall on which the internal window cill sat. Some was probably also dripping down from the internal window cill having been driven in under the lower sash window and up over the base of the window frame (hard to believe but I'd witnessed it happening myself during wet winter Atlantic gales) and pooled on the window cill. Once the moisture was caught behind the poured cement wall there was no way for it to evaporate internally and the joist ends were left sitting in constant damp cement and rubble.
I was pretty comfortable that the cause of the rotting would not persist given the work that had been (and was being) done to make the walls of the house breathable inside and out. Also, the windows had been re-inserted after repair back in '14 sittin up on stone upstand slips that Kevin had cut and put in place to create a proper drip gap under the window frame - rectifying something which hadn't been there previously.
But what were we to do to repair the rotting which had taken place? The builders has seen injection treatment of joist ends tried in other cases. Pete however was very clear: no wasting effort on chemicals, just get timber dry and support joists by picking them up and holding them into the wall. Steel flitch plate or steel shoes were both options. In the end, because the rotting was very localised to the end of the joists and the joists themselves were only 15 years old and supported by other unaffected floor joists, we just doubled them up at the end by bolting with stainless steel bolts a metre of new joists alongside. The main casualty was a metre depth of bedroom floorboards.
Just to make absolutely certain that these joists sit in future cleanly on dry stone with nothing but air around them, we will this winter (following Pete's advice) come at them from the ground floor and clear out any remaining rubble and concrete at their base and leave them lying cleanly on stressline concrete lintels.
And to replace the poured cement wall? We considered a number of options for breathable insulating layers to fill out the very thin stone wall sections under those windows - including expanded cork board with lime plaster. In the end we thought: why not use the leftover sheep's' wool (from the attic insulation) packed behind simple wooden window front boards?
Of course, a wooden board is only breathable if you don't slap acrylic or other synthetic paint on it. And breath-ability would continue to be important here. I am fatalistic that windows facing Atlantic gales full brunt will ship some water no mater what you do. And winter rain lashing against lime render on a thin section of wall will lead to periods when most, if not all, of that thin wall will be damp - until the same strong winds dry the wall out through evaporation. Cue conversation with carpenter:
'Have you ever used linseed paint? No.'
'Are you willing to try it if I get you some? Yes'
The good news was that - unlike the never ending saga of trying to dry the linseed paint on hard teak window frame wood from which acrylic paint had been partialy chemically stripped in 2014 - the linseed paint actually dried pretty easily this time. Why? Firstly it was new untreated wood (maple) more receptive to absorbing paint (including a primer coat that was 50% oil). Secondly, the carpenter happened to have a drying cabinet that featured both UV lamps and blown airflow - perfect for linseed paint!
Next post: I'm not sure yet but plenty still to do!